Lightweight and Flexible Cotton Aerogel Composites for Electromagnetic Absorption and Shielding Applications

Abstract

As we realized, shielding and absorption are two effective strategies to weaken the negative effect from unwanted EM radiations. [2] However, the reported works about EM wave shielding and absorption are usually non-correlated, that is, the material with excellent microwave absorption performance owns poor microwave shielding effectiveness, and vice versa. [3] This is mainly attributed to their very different working principle. [4] Hence, one material with two microwave functions may be the development trend for solving microwave interference issues. For EM wave shielding, the surface reflection and internal absorption are the main contributions to shield incident microwave. [5] Most of shielding efficiency depends on the surface reflection, so excellent conductivity is a prerequisite for high shielding performance. For example, a sponge structure of the Ag@C nanowires reported by Wan et al. demonstrates the good electrical conductivity of 363.1 S m −1 and amazing EM shielding effectiveness (SE) of 70.1 dB in 8.2-18 GHz. They deduced that the reflection should be responsible for the outstanding shielding properties. [6] By increasing the dispersing of carbon nanotubes (CNTs) in polymer matrix, the CNT-polymer composite shows a high SE value of 29 dB, which ascribed to the high conductivity from the CNTs. [7] As for EM wave absorption, the microwave should first enter the interior of the absorber, then attenuated to thermal or other forms of energy, which desires superior impedance match behavior and attenuated capacity. According to free electron theory, the excessive or poor conductivity would cause the incident microwave to be reflected or not dissipated. [8] This theory illustrates that conductivity has a positive effect on the permittivity. If the conductivity is too high, the excessive permittivity would give rise to poor impedance matching. Thus, most of the incident EM waves would be reflected back, leading to poor microwave absorption. [9] Conversely, the low conductivity would result in small permittivity. Although this is favorable for the impedance matching, the EM attenuation ability would be reduced. The incident EM wave could not be consumed by materials, bringing about poor microwave absorbing property. [10] Hence, to obtain excellent microwave absorption performance, moderate conductivity is desired, which could effectively balance the impedance matching and attenuation ability. For instance, Yang et al. prepared the NiCo 2 / graphene nanosheets (NiCo 2 /GNS) composites with different Currently, a versatile route is urgently required to achieve excellent electromagnetic wave (EMW) absorption and shielding functions simultaneously. A lightweight, flexible and sustainable 3D framework aerogel is designed to reach this goal, which is assembled by unique "1D-1D" combination, nanoscale carbon nanotubes (CNTs) grown on microscale carbon fiber. EM absorption requires appropriate conductivity of filler to acquire moderate permittivity. On the contrary, EM shielding requires great conductivity to reflect m...

Improved impedance matching by multi-componential metal-hybridized rGO toward high performance of microwave absorption

“…To investigate the MA performance of the McM@rGO hybrids, frequency-dependent electromagnetic parameters are measured. The real parts of permittivity (ε′) and permeability (μ′) represent the storage ability of field energy, whereas the imaginary parts of permittivity (ε″) and permeability (μ″) indicate the dissipation capacity [42][43][44][45]. The complex permittivities of these synthesized hybrids are given in Figure 5(a and b).…”

Porous carbon materials for microwave absorption

“…Recently, carbon foams (CFs) or carbon aerogels with open-hole network structures have attracted great attention as potential microwave absorbers due to their advantages such as low density, outstanding electrical transport property, high surface area and excellent mechanical stability. 60,61,[118][119][120][121][122][123][124] Unfortunately, pure PC-based foams/aerogels are seriously limited by their strong conductivities, resulting in poor impedance matching. It is vital to integrate them with other materials to tune the electromagnetic parameters and impedance matching.…”

“…Directly integrating other materials into one foam or aerogel during their fabrication process is also an important way to improve the MA performance of pure PC-based foam/aerogel absorbers. 60,118,[121][122][123] Zhao et al fabricated Ni 2+ /alginate foams as precursors and then pyrolyzed them to get lightweight porous Ni/carbon foams (B0.1 g cm À3 ) 123 (Fig. 6a).…”

“…Similarly, Cheng et al used cotton fibers as 3D scaffolds, and then sequentially coated with Co 2+ and dicyandiamide (DCDA). 121 After thermal pyrolysis, the metal Co generated as a catalyst could promote the growth of CNTs on the carbon fiber (Fig. 6b).…”

Hybrid structured CoNi2S4/Ni3S2 nanowires with multifunctional performance for hybrid capacitor electrodes and overall water splitting

“…The as-prepared samples exhibited a specic capacitance of 1192 mF cm À2 at 2 mA cm À2 and cycle stability. 18 Liu and co-workers prepared NiCo 2 O 4 nanowires through a simple hydrothermal process; the as-prepared samples showed excellent electrocatalytic performance with an overpotential of 320 mV at 10 mA cm À2 . 19 However, single metal oxide electrode materials oen present poor electrical conductivity, which limits the electrochemical performance.…”